The present invention relates to a sealing structure for an outboard motor.
A conventional small-size outboard motor is shown in FIG. 11, in an state to be mounted to a hull, as a right-hand side view, the outboard motor being mounted with a four-stroke-cycle engine. In FIG. 11, an outboard motor 100 comprises an engine 101 having a lower portion in which an oil pan 102 and a drive-shaft housing 103 are vertically disposed. The engine 101 and the oil pan 102 are covered with an engine cover unit 104.
The engine cover unit 104 is made of synthetic resin and composed of a lower cover 104a secured to the oil pan 102 and an upper cover 104b detachably joined above the lower cover 104a, which is formed to be separated into right and left cover sections.
A waterproof sealing portion 105 is provided for the lowermost portion of the lower cover 104a. The waterproof sealing portion 105 fluid-tightly seals between the lower end of the lower cover 104a and the oil pan 102 to prevent introduction of water from outside. Thus, the water-proof sealing portion 105 makes the engine 101 and oil pan 102 to be waterproof.
The oil pan 102 has a plurality of external access portions such as a drain hole 106 for discharging oil and a mounting frame 107 for receiving a mounting portion, not shown, for establishing the connection between the overall body of the outboard motor 100 and the hull. The waterproof sealing portion 105 is arranged below the external access portions 106 and 107.
FIG. 12 is an enlarged view of the waterproof sealing portion 105. As shown in FIG. 12, upper and lower horizontal ribs 109 and 110 projecting inwards are formed in the lowermost portion of the lower cover 104a around the inner surface thereof. An outer portion of a seal portion 111 made of an elastic material, such as rubber, is held between the upper and lower horizontal ribs 109 and 110.
On the other hand, two stepped portions 112 and 113 are formed in the upper portion of the drive-shaft housing 103. The inner portion of the seal portion 111 is received in a groove 115 formed between the upper step 113 and a flange 114 formed at the lowermost end of the oil pan 102. Thus, the space between the lower cover 104a and the oil pan 102 is made to be waterproof.
However, in the above-mentioned conventional structure, it is necessary to locate the upper and lower horizontal ribs 109 and 110 which are formed in the lowermost portion of the lower cover 104a around the inner surface thereof. Therefore, the lower cover 104a cannot easily be molded and thus the manufacturing yield becomes unsatisfactory. Furthermore, the necessity of inserting the seal portion 111 into a space between the upper and lower horizontal ribs 109 and 110 makes worse the assembling workability.
The upper and lower horizontal ribs cause the weight of the lower cover of a large-size outboard motor to be enlarged, and furthermore, there arises a problem in that the upper and lower horizontal ribs requiring large spaces prevent arbitrary layout.
The lower cover 104a has access holes, not shown, in FIG. 11 corresponding to the external access portions which are the drain hole 106 of the oil pan 102 and the mounting frame 107. Since the waterproof sealing portion 105 is formed below the above-mentioned access holes, waterproof sealing structures must be provided for the access holes to prevent introduction of water into the lower cover 104a. Therefore, the multiplicity of the sealing structures result in the increasing of the number of elements to be disposed and the increasing of labour of workers.